Flexible electrode antenna

ABSTRACT

The invention provides a flexible electrode antenna having a layer of conductive material laminated between a layer of flame retardant material and a layer of protective material. The layer of conductive material is preferably a metalized polymer substrate having corrosion resistant properties. The flame retardant material is preferably a glass cloth, while the protective material is preferably a non-woven material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/169,267, filed Jun. 27, 2002, now U.S. Pat. No. 6,683,583, which wasa national stage filing under 35 U.S.C. 371 of PCT/US01/04057 filed Feb.8, 2001, which International Application was published by theInternational Bureau in English on Aug. 16, 2001, which claims priorityto U.S. Provisional application No. 60/182,089 filed Feb. 11, 2000.

BACKGROUND

The present invention relates to electrode antennas, and particularly toan electrode antenna with sufficient reliability, flexibility anddurability for use as a sensing element in a system for sensing thepresence of a person in a defined space.

As discussed, for example, in U.S. Pat. Nos. 5,914,610 and 5,936,412,the ability to determine the position, orientation or presence of aperson within a defined space is important in applications ranging frommedical treatments to safety and security. For applications wheredetermining the position, orientation or presence of a person within adefined space is important, sensor arrays have been developed to allowautomatic monitoring of the defined space. Such sensor arrays andmethods for resolving a presence in a defined space are taught in theabove-referenced patents.

Although the method for resolving a presence or activity in a definedspace using sensor arrays is known, the ability to adapt those sensorarrays to a particular environment is not addressed in the prior art.Specifically, in uses where the sensor array is used to monitor ordetect the presence or activity of a person, additional factors comeinto play which may greatly impact the acceptance of the sensor array bythe individual being sensed. For example, an expected use of thesesensor arrays and methods as described in U.S. Pat. Nos. 5,914,610 and5,936,412 is in an automobile seat for regulating the deployment ofairbags. While any variety of electrodes may work suitably for detectingthe position, orientation or presence of a person within the automobileseat, if the presence of the sensor electrodes is uncomfortable to theperson in the seat, or creates an excessive cost in the production ofthe automobile, it is less likely that such a system will be accepted bythe ultimate purchaser and user of the automobile.

In applications such as sensors in an automobile seat, or otherapplications where the sensor is placed in close proximity to anindividual, factors such as the sensor flexibility, comfort anddurability are critical for successful use and acceptance of the sensorarray in the intended application. The sensor must be flexible becauseit is being placed in a flexible or resilient medium (such as a seatcushion), it must be comfortable (undetectable) to the user, and it mustbe durable so that it does not need to be replaced during the life ofthe object in which it is placed.

In addition, because it is anticipated that the sensor will be used inhigh volume applications, it is important that its construction beequally capable of high volume and low-cost production.

SUMMARY OF THE INVENTION

The present invention provides a flexible conductive electrode antennawhich may be manufactured in high volume and at low cost, while stillproviding the necessary characteristics of flexibility, flameretardancy, corrosion resistance, abrasion resistance, tear resistance,and electrical reliability. The invention comprises a laminatedconstruction having a layer of conductive material laminated between alayer of flame retardant material and a layer of protective material.The layer of conductive material is preferably a metalized polymersubstrate having corrosion resistant properties. Preferably, the polymeris metalized on one side with a layer of copper disposed between layersof nickel. The flame retardant material is preferably a glass clothlaminated to the non-metalized side of the polymer substrate. Theprotective material is preferably a non-woven material laminated to themetalized side of the polymer substrate.

In an alternate embodiment, the layer of conductive material maycomprise a conductive woven or conductive non-woven material. Also, theflame retardant layer may comprise an epoxy tape having a fire retardantcomponent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically illustrate a preferred construction of theelectrode antenna in a partially exploded and assembled condition,respectively;

FIG. 2 schematically illustrates an alternate embodiment of theelectrode antenna;

FIGS. 3A-3D schematically illustrate the manufacture of the electrodeantenna of FIGS. 1A and 1B;

FIG. 4 illustrates a creasing machine for testing the electrode antenna;

FIG. 5 schematically illustrates an alternate embodiment of theelectrode antenna schematically;

FIGS. 6A-6C show various sensor shapes after being cut from the sensortape material.

DETAILED DESCRIPTION OF THE INVENTION

Although those skilled in the art will readily recognize that multipleunique constructions may be created for use as a flexible sensorelectrode, the present invention is described herein primarily inrelation to one preferred construction. In particular, the presentinvention is described herein as a flexible sensor electrode having afilm-fabric lamination construction (see FIGS. 1A and 1B). In addition,alternate constructions in addition to those described herein areconsidered within the scope and spirit of the invention.

In a preferred embodiment of sensor tape 10 illustrated in FIGS. 1A and1B, a polyester (PET) film 12 is provided as a carrier substrate tofabricate the conductive layer 14 of the sensor tape. Specifically,layers of nickel 16, copper 18 and then nickel 20 are deposited on thesurface of the polyester film 12 by any suitable means known in the art.The preferred method of metalizing the substrate 12 is by vapordeposition, but other suitable methods include electroplating, andconductive ink printing, for example. The polyester film 12 providessufficient flexibility for the final use of the sensor tape 10, while italso has sufficient rigidity for use in the metal deposition process.The nickel layers 16, 20 on either side of the copper layer 18 providebetter adhesion to the polyester film substrate 12 than copper alone andalso serve as corrosion protection layers for the copper layer 18. Thecopper layer 18 provides excellent electrical conductivity to allow theconstruction to act as a sensor or antenna. The thickness of the nickellayers 16, 20 is preferably in the range from 250 to 600 angstroms, andthe thickness of the copper layer 18 is in the range from 2000 to 3000angstroms. More preferably, the nickel layers 16, 20 are approximately400 angstroms thick and the copper layer 18 is approximately 2500angstroms thick. The preferred ranges of material thickness allow adesired balance of material flexibility and reliability, while providingadequate amounts of material for electrical conductivity and corrosionprotection. If desired, an all nickel construction of the conductivelayer (e.g., no copper layer) on the polyester film may also be used, inplace of a nickel-copper laminate as described above.

Using the polyester substrate 12 with copper and nickel metalizinglayers as described above (“nickel-copper laminate 22” herein), severalunique sensor tape constructions may be produced. Examples of these ofthe different types of tape constructions include: laminating thenickel-copper laminate 22 to epoxy film tapes 32 (FIG. 2) and laminatingthe nickel-copper laminate to glass cloth fabric 30 to provide inherentflame retardency, flexibility, and puncture and tear resistance (FIG.1B). In certain applications, it may be desired to use specializedadhesives, such as A25 high performance adhesive (available from 3M) topermit adhesive bonding to polyethylene film, such as those used in carseat construction.

A25 High Performance Adhesive is made by Minnesota Mining andManufacturing Company (3M) of St. Paul, Minn., USA. This adhesive isideal for joining a wide variety of similar and dissimilar materialswhere high bond strength, high shear strength, high temperatureperformance and good UV resistance are required. A25 High PerformanceAdhesive is a firm acrylic pressure sensitive adhesive system.

As noted above, the preferred construction is shown in FIGS. 1A and 1B.In addition to the nickel-copper laminate 22 described above, theelectrode antenna preferably includes a reinforcement and flameretardant layer 34 and a protective layer 36 over the nickel-copperlaminate 22. Preferably, the nickel-copper laminate 22 is positionedbetween the reinforcement and the flame retardant layer 34 and theprotective layer 36 to maximize the protection afforded to thenickel-copper laminate layer 22.

As seen in FIGS. 1A and 1B, the reinforcement and flame retardant layer34 preferebly comprises a layer of glass cloth 30 with an adhesive 38(either a heat sensitive adhesive (HSA) or a pressure sensitive adhesive(PSA)) used to bond the glass cloth 30 to other parts of theconstruction. A suitable glass cloth 30 is blown glass fiber (BGF)cloth. A suitable adhesive 38 is the A25 high performance adhesivesystem available from Minnesota Mining and Manufacturing Company. Aremovable and disposable release liner 40 may be used to protect theadhesive 38 prior to the final lamination of the sensor tape assembly10.

The protective layer 36 preferably comprises a layer of non-wovenmaterial 42 such as PET, or any other suitable nonwoven material, suchas rayon or Teflon®. An adhesive layer 44 is used to bond the protectivelayer material 42 to the nickel-copper laminate 22. A non-woven materialis preferred because such a material is flexible and breathable. Apreferred non-woven material is available from Minnesota Mining andManufacturing Company under the designation 1157R tape. 1157R tape is aporous 100% Rayon non-woven fiber backing tape. 1157R tape isspecifically designed to allow thorough penetration of the impregnatingresin inside bobbin-wound coils. An acrylic adhesive is preferably usedwith the 1157R nonwoven material. Another advantage of the preferred1157R tape is its ability, because of its porosity, to pick up resin andbecome thicker, making a hard moisture and mechanical barrier. Theprotective layer 36 preferably uses a water-based acrylic adhesive suchas the adhesive available under the designation RD814 from MinnesotaMining and Manufacturing Company. Alternate adhesives include acryliciso-octylacrylate/acrylic acid (IOA/AA) or 2-ethylhexyl acrylate/acrylicacid (EHA/AA) with corrosion inhibitor additives. A removable anddisposable release liner 46 may be used to protect the adhesive 44 priorto the final lamination of the sensor tape assembly 10.

The preferred process for constructing the tape sensor construction ofFIGS. 1A and 1B is shown in FIGS. 3A-3D. As illustrated in FIGS. 3A-3Crespectively, the protective layer 36, the nickel-copper laminate layer22, and the reinforcement fire retardant layer 34 are individuallyformed. In FIG. 3A, a non-woven protective material 42 is coated withadhesive 44 and then laminated with a release liner 46. After thelamination, the assembly may be punched to create any openings needed inthe final sensor construction. In FIG. 3B, a PET substrate 12 ismetalized to create the nickel-copper laminate 22. In FIG. 3C, areinforcing and fire retardant glass cloth 30 is laminated betweenlayers of adhesive 38. A release liner 40 is also included in thelamination to protect the adhesive layer 38 until the final laminationstep.

After the individual protective layer 36, nickel-copper laminate layer22, and reinforcement fire retardant layer 34 are created, theseseparate elements 36, 22, 34 are laminated together as shown in FIG. 3D.A final slitting or cutting process creates the individual sensors whichmay then be used for their intended purposes.

The sensor construction described herein has numerous advantages for itsintended use. Those advantages are described in greater detail below.

Flexibility

An advantage of the above-described sensor construction 10 is itsinherent flexibility, conformability and durability. To demonstrate theflexibility of the flexible electrode tape 10 described herein,individual sensors were created as described above and crease-flextesting was performed. The crease-flex testing used a creasing machineas illustrated in FIG. 4. The creasing machine used a creasing stroke of50 mm, a pressing load of 9.8 N (1 kilogram force) and a creasing speedof 120 strokes/minute. The creasing machine was used to repeatedlycrease samples of the flexible electrode antenna described herein, aswell as alternative electrode antenna constructions. The tests wereperformed by placing two test samples 58 of sensor material of the samesize (approximately 2 inches by 6 inches in size) with the glass clothside on the outside of the crease. The samples were positioned so thatthe crease formed across the shorter dimension of the sample. Thedistance between the clamping members 60 was gradually decreased byapplying a pressing load in the direction of arrow A so that the twotest samples 58 creased until the folded sample came into contact withitself. The creasing test then proceeded with test load applied. Theelectrical resistance between the farthest points on the test samples 58was checked after every 120 creasing cycles. The results of the testsare shown in Tables 1-2 below. The materials tested included theabove-described antenna material with a 1157R tape backing (FIG. 1B) andthe above-described antenna material without a 1157R tape backing (FIG.5).

TABLE 1 Antenna Material - Without 1157R Tape Backing Number of Sample 1Sample 2 Sample 3 Sample 4 Strokes (Ohms) (ohms) (ohms) (ohms 0 .41 .41.4  .43 120 .48 .43 .51 .43 240 .48 .49 .54 .45 360 .49 .51 .54 .48 480.47 .51 .58 .59 600 .60 .58 .57 .63 720 .63 .59 .61 .63 840 .64 .61 .59.66 960 .66 .61 .69 .67 1080 .66 .67 .65 .65 1200 .67 .63 .64 .65

TABLE 2 Antenna Material - With 1157R Tape Backing Number of Sample 1Sample 2 Sample 3 Sample 4 Strokes (ohms) (ohms) (ohms) (ohms) 0 .45 .40.41 .37 600 .50 .47 .51 .60 1200 .61 .68 .55 .63Flame Retardancy

Because the sensor described herein is anticipated for use inautomobiles and other applications where flame retardancy is desired orrequired, flame retardant testing was conducted following FM VSSN302test standards, with the results shown in Table 3.

TABLE 3 Material Burn Rate Observation Conductive layer 2.3inches/minute Pass test standard laminated to a glass cloth Conductivelayer 3.8 inches/minute Pass test standard laminated to an epoxy tapewith fire retardant backing Conductive layer 3.6 inches/minute Pass teststandard laminated to a glass cloth and A25 adhesive system Conductivelayer 5.9 inches/minute Fail test standard laminated to an epoxy tapewith fire retardant backing and A25 adhesive system

The epoxy tape with fire retardant backing is available from MinnesotaMining and Manufacturing Company under the designation 3M #1 electricaltape. As can be seen from the test results, the glass cloth fabric hasan inherent flame retardant property which makes the total constructionof the prototype using glass cloth in the construction pass flammabilitytests under the cited test standard.

Abrasion Resistance

Abrasion testing on the conductive surface of the sensor tape wasconducted by preparing circular samples of the sensor tape. Each samplehad a 4.1 inch (10.4 cm) diameter and a 6 mm diameter hole in the centerof the sample. Samples with and without a protective layer 36 wereprepared. The protective layer 36 consisted of a non-woven materialadhered to the conductive surface with an acrylic adhesive. Thenon-woven acrylic tape used in the test was 1157R tape available fromMinnesota Mining and Manufacturing Company. The initial electricalresistance of each sample was recorded by placing one electrical probenear the hole in the center of the sample and another electrical probeat the outer circumference of the sample. A Taber abraser machine(available from Taber Industries of North Tonawanda, N.Y. USA) was usedto abrade the samples in the following manner: The test samples wereplaced on the abraser holding apparatus with the conductive layer of thesensor tape facing up. A CS10 abrasion wheel (available from TaberIndustries) was installed on the abraser machine and a test load appliedto the wheel. 1,000 cycles were performed with the abraser machine.After the abraser machine had stopped, the electrical resistance of thesample was again tested by placing one probe at the edge of the centerhole of the sample, and the second probe at the outer edge of thesample. The results of the abrasion testing are shown in Table 4.

TABLE 4 Final Result Sample Description Load Initial ResistanceResistance No protective layer 0.25 kgf 0.65 Ω  15.5 Ω No protectivelayer 0.50 kgf 0.65 Ω 2.000 Ω With protective layer 0.25 kgf 0.65 Ω 0.65 Ω With protective layer 0.50 kgf 0.65 Ω  0.65 Ω

As can be seen from the abrasion test data, the addition of a non-wovenprotection layer with an acrylic adhesive on the top of the conductivesurface of the sensor tape provides adequate protection to theconductive layer to prevent the conductive layer from being abraded. Theload used in the abrasion testing has no effect when the 1157Rprotective layer is incorporated into the construction. Without theprotective layer 36, the load has a significant effect on the finalresistance of the test sample. After the abrasion test, the nickelprotective layer 20 could not be detected when the non-woven acrylictape protective layer was not used. The removal of the nickel layer 20would result in poor corrosion protection for the copper layer 18. Thus,after exposure to room temperatures and humidity the exposed copperlayer 18 would eventually corrode completely and fail.

Electrical Resistance Reliability

Electrical resistance testing was conducted for multiple samples of thesensors to demonstrate the consistency and reliability of the inventiveconstruction described herein. The results of the resistance testing areshown in Table 5.

The designations LR1, LR2, etc. designate different sensor shapes. Ascan be seen, the resistance reading for each sensor is well under 1Ω,which is important for the use of the sensor in its intendedapplications. It is preferred to maintain the resistance for individualsensors below 1Ω so that the sensors are suitable for use in a systemthat requires extensive signal processing. Low resistance also minimizespower drainage, and provides a high differential from the surroundinginsulation material in areas of high humidity (such as when anautomobile seat is wet from spilled liquid). The resistance readingswere taken from the farthest points in each sensor.

TABLE 5 Electrical Resistance (Ohm) Sample No. LR1 LR2 LR3 LR4 UR5 UR6SR7 A1 0.5 0.3 0.4 0.4 0.5 0.5 0.4 A2 0.5 0.4 0.4 0.4 0.5 0.5 0.4 A3 0.50.4 0.4 0.4 0.5 0.5 0.4 A4 0.6 0.4 0.4 0.4 0.5 0.5 0.4 A5 0.4 0.4 0.40.4 0.5 0.6 0.4 A6 0.5 0.4 0.4 0.4 0.5 0.5 0.4 A7 0.6 0.3 0.4 0.4 0.50.5 0.4 A8 0.5 0.5 0.5 0.5 0.5 0.5 0.4 A9 0.5 0.4 0.4 0.4 0.6 0.5 0.5A10 0.6 0.4 0.5 0.5 0.5 0.5 0.4 A11 0.4 0.4 0.4 0.4 0.4 0.5 0.4 A12 0.50.4 0.4 0.4 0.4 0.4 0.4 A13 0.6 0.4 0.4 0.4 0.4 0.4 0.4 A14 0.5 0.3 0.40.3 0.5 0.4 0.4 A15 0.5 0.4 0.5 0.4 0.5 0.4 0.4 A16 0.4 0.4 0.4 0.4 0.50.4 0.5 A17 0.5 0.4 0.4 0.4 0.5 0.5 0.4 A18 0.6 0.5 0.4 0.4 0.5 0.5 0.4A19 0.5 0.4 0.3 0.4 0.5 0.5 0.4 A20 0.5 0.4 0.4 0.4 0.5 0.5 0.4 A21 0.50.4 0.4 0.4 0.4 0.5 0.4 A22 0.4 0.4 0.4 0.4 0.6 0.5 0.5 A23 0.5 0.3 0.40.4 0.5 0.5 0.4 A25 0.5 0.4 0.4 0.4 0.5 0.5 0.4 A26 0.5 0.4 0.4 0.4 0.50.5 0.4 A27 0.5 0.4 0.4 0.4 0.5 0.5 0.3 A28 0.6 0.4 0.4 0.4 0.5 0.5 0.4A29 0.5 0.4 0.4 0.4 0.5 0.5 0.4 A30 0.5 0.4 0.5 0.4 0.5 0.5 0.3 A31 0.40.4 0.5 0.5 0.5 0.5 0.4 A32 0.5 0.4 0.5 0.5 0.6 0.5 0.4 A33 0.6 0.4 0.50.5 0.6 0.6 0.4 A34 0.5 0.4 0.5 0.5 0.5 0.6 0.4 A35 0.5 0.4 0.4 0.4 0.50.4 0.4 A36 0.4 0.4 0.3 0.4 0.5 0.4 0.4 A37 0.5 0.4 0.3 0.3 0.5 0.5 0.4Avg. Type A 0.503 0.394 0.411 0.408 0.603 0.488 0.403 B1 0.5 0.5 0.4 0.40.5 0.5 0.4 B2 0.5 0.4 0.4 0.4 0.5 0.5 0.4 B3 0.5 0.4 0.4 0.4 0.5 0.50.4 B4 0.4 0.3 0.4 0.4 0.5 0.5 0.4 B5 0.4 0.4 0.4 0.4 0.5 0.6 0.4 B6 0.50.4 0.4 0.4 0.5 0.5 0.5 B7 0.4 0.4 0.4 0.4 0.5 0.5 0.5 B8 0.5 0.4 0.40.4 0.5 0.5 0.3 B9 0.6 0.4 0.4 0.4 0.4 0.5 0.3 B10 0.5 0.3 0.3 0.3 0.40.5 0.3 B11 0.5 0.5 0.4 0.4 0.4 0.5 0.4 B12 0.5 0.4 0.4 0.4 0.6 0.5 0.4B13 0.5 0.4 0.4 0.4 0.5 0.6 0.4 B14 0.5 0.4 0.4 0.4 0.6 0.6 0.4 B15 0.40.4 0.4 0.4 0.4 0.4 0.4 B16 0.4 0.4 0.4 0.4 0.5 0.5 0.4 B17 0.6 0.4 0.40.4 0.5 0.5 0.4 B18 0.5 0.4 0.4 0.4 0.5 0.5 0.4 B19 0.5 0.4 0.4 0.4 0.50.5 0.4 B20 0.5 0.3 0.4 0.4 0.5 0.5 0.4 B21 0.5 0.3 0.3 0.4 0.6 0.6 0.5B22 0.5 0.5 0.4 0.4 0.5 0.5 0.3 B23 0.5 0.4 0.4 0.4 0.4 0.4 0.3 B24 0.40.4 0.4 0.4 0.6 0.6 0.3 B25 0.4 0.4 0.4 0.4 0.5 0.5 0.3 B26 0.5 0.4 0.50.5 0.5 0.5 0.3 B27 0.6 0.4 0.4 0.4 0.5 0.5 0.4 B28 0.5 0.5 0.4 0.5 0.50.5 0.4 B29 0.5 0.4 0.4 0.4 0.5 0.4 0.4 B30 0.5 0.4 0.4 0.4 0.4 0.6 0.4B31 0.6 0.4 0.4 0.4 0.4 0.4 0.4 B32 0.5 0.5 0.4 0.4 0.5 0.5 0.4 B33 0.50.3 0.5 0.5 0.5 0.5 0.4 B34 0.5 0.3 0.3 0.3 0.5 0.5 0.4 B35 0.5 0.4 0.40.4 0.5 0.5 0.4 B36 0.4 0.4 0.4 0.4 0.4 0.4 0.5 B37 0.4 0.4 0.4 0.4 0.60.6 0.3 Avg. Type B 0.486 0.397 0.397 0.403 0.492 0.505 0.386 C1 0.5 0.40.4 0.4 0.5 0.5 0.4 C2 0.5 0.4 0.4 0.4 0.5 0.5 0.4 C3 0.5 0.4 0.4 0.40.5 0.5 0.4 C4 0.5 0.4 0.4 0.4 0.5 0.5 0.4 C5 0.4 0.4 0.4 0.4 0.5 0.50.5 C6 0.5 0.4 0.4 0.4 0.4 0.4 0.3 C7 0.5 0.4 0.4 0.4 0.5 0.5 0.4 Avg.Type C 0.486 0.400 0.400 0.400 0.486 0.486 0.400 D1 0.6 0.4 0.4 0.4 0.50.5 0.4 D2 0.5 0.3 0.3 0.3 0.5 0.5 0.4 D3 0.5 0.5 0.5 0.5 0.5 0.4 0.4 D40.5 0.4 0.4 0.4 0.6 0.6 0.4 D5 0.5 0.4 0.4 0.4 0.5 0.5 0.3 D6 0.5 0.40.4 0.4 0.5 0.5 0.5 D7 0.5 0.4 0.4 0.4 0.5 0.5 0.4 Avg. Type D 0.5140.400 0.400 0.400 0.514 0.500 0.400Tear Resistance

The preferred embodiment of the flexible electrode antenna providesexcellent tear resistance, which is also important in its intended finaluse. Samples of the preferred embodiment were tested following thestandard test method for initial tear resistance of plastic film andsheeting (ASTM D 1004-94A). Following the guidelines of the ASTM testprocedures, failure values in the range from 8.0 to 11.6 lbs. in themachine direction, and 9.7 to 20.7 in the cross direction were obtained.During the testing, the glass cloth fabric did not tear. Rather, thefailure occurred in the metalized film layer. Without the glass clothreinforcement, the metalized film layer failed at between 3.5 and 5.1lbs. As can be seen, the addition of the glass cloth reinforcementsignificantly improves the tear resistance of the samples.

Corrosion Resistance

Because the copper conductive layer will corrode easily with themoisture and heat typically present in an automobile, the corrosionprotection provided by the nickel layer is very beneficial. The effectof the nickel protective layer 16, 20 was demonstrated with tests in ahumidity chamber. Samples of the copper conductive layer 18 with andwithout a nickel protective layer 16, 20 were placed in a humiditychamber at 55° C. with 100% humidity, and the resistance of the sampleswas measured at one week intervals. As can be seen from Table 6, samplesprotected with nickel layers 16, 20 exhibited good resistance tocorrosion (and thus experienced a minimal increase in resistance), whilesamples with no nickel protective layer 16, 20 had resistances whichrapidly increased until the resistance reached infinity. Importantly,the samples which used the nickel protective layer maintained aresistance of less than 1Ω, which is necessary for the intended use ofthe sensor.

TABLE 6 Sample with nickel Sample with no protective protective layerlayer Initial Resistance .56 .60 .60 .45 .50 .45 Ω 1 week Ω .60 .61 .61.75 .75 .85 2 weeks Ω .65 .68 .68 100 600 250 3 weeks Ω .75 .70 .63 20002500 2030 4 weeks Ω .74 .73 .70 ∞ ∞ ∞ 5 weeks Ω .79 .75 .70 ∞ ∞ ∞ 6weeks Ω .79 .89 .72 ∞ ∞ ∞Alternative Embodiment

As an alternative to forming the conductive tape as a film fabriclaminate as described above, the conductive tape could also be formed asa conductive fabric or non-woven material. In this type of construction,the nickel-copper laminate 22 described above would be replaced by aconductive fabric or non-woven material. A fabric or a non-wovenmaterial may be formed of either a conductive material or formed of anon-conductive material which is coated with a conductive material, suchas copper and/or nickel. The fabric would preferably have a tensilestrength of approximately 60 to 70 lbs./inch and a tearing strength ofapproximately 6 to 10 lbs. in both the warp and weft directions. Asurface resistance of 0.10Ω per square inch is desirable. Theconductivity of the conductive material could be promoted by the wet ordry deposition of copper onto the fabric with adequate thickness ofnickel for corrosion protection. The conductive fabric could be furtherfinished with an additional surface coating or lamination to provideflammability resistance or retardance. As with the film fabriclamination concept, the adhesive layer should be aggressive enough toadhere to, for example, polyurethane foam as is used in car seatconstructions.

Separation into Individual Sensors

After the sensor tape has been constructed as described above,individual sensors, as shown in FIGS. 6A-6C, may be formed by, forexample, die cutting the sensors from the tape. The preferred glasscloth backing 30 of the sensor tape 10 provides sufficient rigidity forthe die cutting process, while still maintaining enough flexibility touse the sensor tape in applications where comfort and flexibility aresignificant issues.

Depending upon how the sensors are individually die cut, it may benecessary to separate adjacent sensors by, for example, laser ablation.For example if the die cutting process is used to remove only portionsof the sensor material, such as holes or openings in the sensor, aconductive pathway may still exist between adjacent sensors on the rollof sensor tape. In this instance, laser ablation of the conductivelayers between adjacent sensors may be used to electrically isolate theadjacent sensors. The laser ablation process is well known, and istherefore not described in greater detail herein.

As an alternative to using laser ablation to separate adjacent sensorson the roll of sensor tape, the conductive layer may be first laminatedwith a non-woven protective layer to cover the entire surface of theconductive film, and then the conductive film with its protective layermay be slit into desired widths. The slit conductive film and protectivelayer may then be separated and laminated onto the flame retardant glasscloth backing and spaced as desired. The entire assembly may then belaminated together and the individual antennas die cut to separate theindividual sensors.

A significant advantage of the sensor tape constructions describedherein is their adaptability to multiple sensor configurations, such asto accommodate different seat designs. Because the sensor tape materialmay be easily die cut, it is very easy to change the shape or design ofthe sensor by simply changing the die cutting operation. It is notrequired to construct entirely new sensor tooling for each unique sensorshape.

Although the sensor tape described herein has been described inreference to use in an automobile seat for use with an air bag sensingsystem, other uses will be recognized by those skilled in the art. Forexample, this same type of sensor may be used in, for example, hospitalbeds or other medical equipment, or in any other instance in whichmonitoring of a defined space is required.

1. A flexible electrode antenna having a machine direction and a crossdirection comprising: a layer of conductive material comprising a layerof nickel; a layer of flame retardant material adhered to a first sideof the layer of conductive material; and a layer of non-woven protectivematerial adhered to a second side of the layer of conductive material,wherein the antenna has tear resistance values using test standard ASTMD 1004-94A of from about 8.0 to about 11.6 pounds in the machinedirection, and from about 9.7 to about 20.7 pounds in the crossdirection.
 2. The flexible electrode antenna of claim 1, wherein theflame retardant layer is glass cloth.
 3. The flexible electrode antennaof claim 2, wherein the glass cloth is formed of blown glass fibers. 4.The flexible electrode antenna of claim 1 wherein the protectivematerial is a non-woven PET.
 5. A flexible electrode antenna having amachine direction and a cross direction comprising: a layer ofconductive material comprised of a polymer substrate having a metalizedlayer on a first major surface of the substrate; a layer of flameretardant material adhered to a first side of the layer of conductivematerial; and a layer of non-woven protective material adhered to asecond side of the layer of conductive material, wherein the antenna hastear resistance values using test standard ASTM D 1004-94A of from about8.0 to about 11.6 pounds in the machine direction, and from about 9.7 toabout 20.7 pounds in the cross direction.
 6. The flexible electrodeantenna of claim 5, wherein the metalized layer on the first majorsurface of the polymer substrate comprises a layer of nickel.
 7. Theflexible electrode antenna of claim 5, wherein the metalized layer onthe first major surface of the polymer substrate comprises layers ofnickel and copper.
 8. The flexible electrode antenna of claim 5 whereinthe protective material is a non-woven PET.
 9. The flexible electrodeantenna of claim 5, wherein the flame retardant layer is glass cloth.10. The flexible electrode antenna of claim 9, wherein the glass clothis formed of blown glass fibers.